Axial flow fan improvements

ABSTRACT

An energy efficient and compact axial fan with a housing comprising a fan assembly comprising a drive motor and a propeller coupled thereto. The inlet opening and/or the outlet opening of the fan housing are provided with a shutter assembly positioned adjacent the propeller and having a plurality aerodynamically shaped pivoted louvers working in tandem for less air obstruction and noise. The propeller comprises a plurality of radial blades comprising means for straitening the air flow and reducing the vortex flow of the propeller thereby permitting the shutter to be mounted adjacent the propeller to lessen the dept of the fan housing for making the fan more compact.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed herein relates generally to axial flow fans improvements and, more particularly to axial flow fans having a shutter operated by a centrifugal mechanism for maintaining a controlled environment in buildings such as poultry houses, greenhouses, steel-plants, foundries, etc.

2. Description of the Related Art

Axial flow fans are used to move high volume of air at low static pressure. An application in which they are beneficially used involves the ventilation of poultry house buildings which often are shaped like a tunnel. Intensive rearing of birds (typically more than 10 000) imposes severe demands on the fans which are provided for removing moisture, heat, carbon dioxide and other contaminants from said buildings.

Hot summer days often cause indoor conditions to become much hotter than desired, temperatures above 25 degree Celsius have an adverse effect on production of said birds. The high temperatures can be controlled effectively with large exhaust fans and with water-wetted cooling pads. Typically eight to twelve (48″) propeller fans are installed in one end wall of the building and water-wetted cooling pads are installed on the opposite end wall of said building. When the fans work create a small negative pressure in the building causing outside warm air to pass across the water-wetted cooling pads causing some water to evaporate and extract some heat from the air, thereafter fresh air passes throughout the building cooling said birds.

Most of the conventional fans for use in poultry house buildings applications are propeller type fans comprising a shutter assembly with gravity shutters or vanes extending horizontally across the intake or the exhaust of the fans. Said vanes do not open to a position where they are perfectly horizontal, i.e., the vanes have a slight downward angle thereto because of their weight. In additions the fans are too sensitive to added resistance therefore, a small increase of static pressure causes a substantial reduction of the air flow of the fans. As a result, when wind blows against the fans, the air flow decreases substantially and will not be sufficient to cool the birds which will suffer of heat stress.

To overcome the detrimental effect of the insufficient airflow, a larger number of fans are used. However, the solution is not satisfactory because increases the capital cost and the operating cost due to an increase of energy consumption.

In general, a conventional axial flow fan for agricultural applications includes a housing made of galvanized steel enclosing a drive motor and a propeller which is running adjacent to a venturi or orifice. The fan comprises a shutter assembly provided for preventing infiltration of outside air into the building and back flow through idle fans. Said shutter assembly typically is composed of a myriad of horizontally mounted pivoted vanes connected with cranks and at least one tie rod. As it can be imagined, the large number of vanes constitutes an obstruction to air flow and raise the cost of the fan, which is also increased by the cost of labor required to assemble the large quantity of vanes and elements connecting them.

For maintaining a controlled environment on those poultry house buildings, the fans need to provide an appropriate and precise airflow. Any reduction in needed air flow can reduce bird performance and increases mortalities of the birds. In a conventional axial flow fan with gravity shutters used in a poultry house building dirt can build up on the shutters as fast as a ¼ pound per day and after few days of operation said accumulation of dust causes a reduction of at least 30% of the air flow of the fan and a reduction of air speed in the building of 30%. The lower air velocity causes a significant less cooling for birds.

The shutters or vanes of the fans can be located at the fan intake where ambient air passes across the vanes with low turbulence or can be located at the fan discharge where air flow is more turbulent therefore causing more vibrations and noise. In north climates, for protection from stormy weather the vanes are mounted at the fan intake therefore they open inwardly the fan housing interior therefore the housing is deeper.

In addition, in order to limit the vibrations and noise said vanes must be mounted away from the propeller, of at least of ⅓ of the diameter of the propeller. As a result, the fans are bulkier and heavier and the manufacturing and shipping costs are significantly higher.

The vibrations and noise of said vanes is caused by the interference between the vanes and the vortex flow produced by the propeller, said interference creates a large head pressure that may be prevented providing propellers comprising means producing less turbulent air flow and vanes designed to be less affected by the turbulent air flow. The applicant provides shutter assemblies with a plurality of aerodynamically shaped vanes mounted adjacent the propeller and extending vertically across the intake and/or the exhaust of the fan. The vanes comprise leading edges connected together by a continuous hinge, therefore the vanes work in tandem.

As the vanes are vertically pivoted gravitational dust is prevented from accumulating thereon. As the vanes work in tandem their drag and noise is reduced. However, said vertical vanes have to be operated by an actuator as a centrifugal shutter device. When the fan operates any pressure and energy is required to keep the vanes in their wide open position.

In contrast to prior art fans with shutters comprising a myriad of vanes, the fan of the present invention comprises few vertical pivoted vanes working in tandem therefore the fan is able to move consistently and quietly at least 20% more than the prior art fans. The poultry house fans may operate continuously generating also undesirable noise and vibrations. As such, the fans collectively represent a significant energy drain and source of noise therefore it is important to pay more attention to energy efficiency and reduction of noise level in the design of such fans.

Vibrations and excessive noise of the fans mainly are caused by the air pushed by the propeller and passing across the vanes which oscillate. Another important source of noise is caused by the blades of the propeller which during its rotational movement over obstacles produce a pressure variation on the obstacle which results in noise emission.

As the drive motor is energized, the movement of rotation of the propeller blades imparts to the air a great deal of centrifugal force generating a turbulent air flow that quickly and erratically disperses upon exiting the orifice or venturi that normally surrounds the propeller blades. The turbulent air flow not only comprises a velocity component that is parallel to the propeller blades rotation axis but also a swirl comprised of variable velocity components of various obliquities to the propeller blades rotational axis. Since the function of the propeller blades is to move air in a direction parallel to a rotational axis, velocities imparted in other directions represent degradation in efficiency, increase of the noise and cost to operate the fan.

In particular, the air flow around the tip region of said propeller blades creates a very noisy and strong vortex trailing downstream from the blade tips. To reduce this vortex, it is important to have a very close and uniform clearance between the propeller blade tips and the venturi, so as to minimize the air “leakages” and back air flow.

The applicant solves the problem of vortex production by providing a propeller comprising a hub and plurality of airfoil shaped blades comprising a plurality of fins positioned at the pressure side of the blades. For each propeller blade the applicant provides a radially slidably adjustable shoe comprising a fin extending circumferentially for preventing radial components of the air flow from moving radially toward the venturi, for guiding the air flow substantially axially toward the fan discharge and for preventing air from flowing back around the blades tips. This results in a somewhat more efficient fan capable of operating quietly at a relatively higher static pressure.

The applicant provides also a propeller with a hub and a plurality of airfoil shaped blades comprising a plurality of fins and an outer duct or band secured to the tips of the blades for co-rotation therewith; the blades are pivotally attached to both the duct and the hub. As the duct is attached to the blades tips the creation of vortices and vibrations is reduced. As the vortex generation of the propeller is reduced, if not eliminated, noise is reduced, the problems of air flow interference with the vanes are minimized therefore the vanes can be mounted in proximity of the propeller of the fan. As a result, the novel fan is more compact than prior art fans and it can be delivered to the end user totally assembled. Heretofore, it was necessary to ship a large amount of “air” in the assembled fans at a cost that became significant especially with overseas shipments.

The overall effect of the combination of the improved propellers and improved vanes working in tandem is a noticeable reduction of back pressure on the propeller and a noticeable increase of the efficiency and performance of the fan.

A lower vortex emission also implies that a lower amount of the energy provided to the fan is being spent in the vortex production so that a greater amount of energy can be used to produce useful work in the fluid. Hence, the reduction in the noise level comes with an increase in the fan efficiency.

Another problem encountered with axial flow fans used in poultry house buildings includes the drive belt. Over time, a typical V-belt will eventually wear and the tension transmitted by the belt will vary causing slippage and reduction of fan air flow. Therefore the applicant provides toothed gears and timing belts. End users never have to worry about belt slippage and reduction of the airflow of the fans.

To solve some of prior art problems of the shutters, the applicant previously provided a fan described in U.S. Pat. No. 6,276,895 issued on Aug. 21, 2001, and its teachings are incorporated herein by reference. The fan described in that patent had an exhaust shutter assembly with vanes that did not have insulation or protection from the elements.

To prevent the problem of dust accumulation on shutters, the applicant previously proposed a fan with a shutter assembly having vertically pivoting vanes mounted across the fan housing. Reference of this fan may be found in my U.S. patent pending application Ser. No. 10/679,475 having filing date Oct. 7, 2003 and its teachings are hereby incorporated by reference. Other prior patents which are pertinent to the present application are: U.S. Pat. No. 4,217,816; U.S. Pat. No. 5,195,928; U.S. Pat. No. 5,288,202.

The above patents have been fully described in my referred patent and patent application and show propeller fans comprising a centrifugal mechanism designed to operate positively the shutter vanes which are made of thin metal providing relatively poor insulating qualities, said vanes lack positive seals which do not permit them to be used effectively in severe and cold climate areas.

SUMMARY OF THE INVENTION

The present invention relates to an axial flow fan that is particularly quiet in operation and effectively overcomes the prior art drawbacks.

The first embodiment of the present invention provides an axial flow fan comprising a compact cylindrical housing having an air intake opening comprising a substantial large bell shape mouth, a drive motor for rotating a propeller secured to a fan bracket comprising four intersecting arms secured to four opposite sides of said input portion of said fan housing and to a bearing case for rotatably holding a rotating shaft to which are secured the propeller and a pulley coupled to said drive motor via a toothed belt.

The drive motor is mounted on a pair of L shaped supports slidably mounted on said bracket such that the weight of the drive motor tightens the toothed belt. The fan housing further comprises a spaced apart outlet or discharge opening comprising a shutter assembly and a discharge cone.

The propeller comprises a hub which is secured to said shaft for rotatably holding a plurality of airfoil shaped blades, each of which comprising a stem journaled into said hub. Each airfoil blade comprises a plurality of fins and a radial adjustable shoe comprising a circumferential extending fin configured for directing the air flow axially with reduced swirls. Said shutter assembly comprises a pair of vertically pivoted doors, semi-circular in form, positioned vertically across the outlet opening of the fan housing. The doors are coupled by a pair of gears for simultaneous movement in opposite directions, so as to move between open and closed positions to close or to open the discharge opening. The shutter assembly further comprises biasing means to maintain positively wide open the doors upon fan rotation. The shutter assembly is normally operated by a centrifugal mechanism secured to the aforesaid rotating shaft and positioned adjacent the propeller. The centrifugal mechanism comprises at least two centrifugal masses operatively connected to an axial sliding reciprocating actuator comprising operative biasing means to maintain positively closed the doors when the fan is not in use.

When the drive motor is energized, the doors are quickly and quietly opened by the air flow produced by the propeller and when the drive motor is off, the doors are firmly closed by the operative biasing means.

The second embodiment of the present invention provides a fan with a compact cylindrical housing similar to the one previously described but the centrifugal mechanism comprises a push rod secured to a bearing case comprising bearing means adapted to push and to pull the shutter doors via a pair or arms, causing their opening and their closing.

The third embodiment of the invention provides a fan with a compact square shaped housing and a shutter assembly comprising a plurality of pair of vertical mounted vanes vertically extending across the outlet opening of the fan and having leading edges connected each other with a hinge. The vanes work in tandem and are operated by a centrifugal mechanism via a roller bearing connection. A propeller is provided with a plurality of airfoil shaped blades comprising an outer circular band bolted to the tip portions of said blades to lessen the known vortices, vibrations and noise. The fan housing is very compact and comprises an intake bell mouth having a round portion mounted coaxially to the outer circular band of said propeller for guiding smoothly the ambient air for best efficiency and low noise. The fan further comprises a discharge duct for protecting the shutter assembly and permitting moisture to be evacuated away from the fan housing.

The fourth embodiment of the present invention provides a fan with a cylindrical housing comprising an intake opening and an output opening, a drive motor secured to a bracket rotatably supporting a hollow shaft on which are secured at least a propeller assembly and a centrifugal actuator. The propeller comprises a plurality of blades pivotally secured to a split hub, each of said blades is provided with a radial adjustable shoe mounted at the blade tip thereof. The discharge end of the fan is provided with a shutter assembly comprising a plurality of evenly angularly spaced pair of hinged vanes arranged to work in tandem. Thus provided, when the fan is on, all pair of vanes are able to rotate simultaneously and silently to their wide open position such as to assume a position parallel to the air flow. Each of the vanes comprises means for rotatably connecting them to the aforesaid centrifugal actuator.

OBJECT OF THE INVENTION

It is an important object of the present invention to teach certain additional unique improvements upon the fans taught by the applicant in U.S. Pat. No. 6,276,895 and co-pending U.S. patent application Ser. No. 10/679,475.

A further object of the invention is to provide a high efficiency fan comprising a shutter assembly comprising vanes operated by a centrifugal mechanism.

A further object is to provide a maintenance free axial flow fan suitable to work at higher static pressure to move efficiently, quietly and consistently large quantities of air.

Another object of this invention is to provide an axial flow fan that is strong, compact and durable, comprising few parts that can be quickly assemble.

Another important object of this invention is to provide a low noise fan with a positive drive comprising a synchronous drive belt.

Other features, advantages and the manner in which the foregoing objectives and advantages of the invention may be best achieved will be more fully understood from the following description when read in conjunction with the accompanying drawings which illustrate the preferred embodiments of the invention by a way of example

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the invention, briefly summarized above, may be added by reference to the embodiments thereof which are illustrated in the appended drawings and described herein. It is to be noted, however, that the appended drawings illustrate only some embodiments of the invention and are therefore not be considered limiting of its scope, because the invention may admit to other equally effective embodiments.

FIG. 1A shows a fragmentary rear view (intake side) of the axial flow fan 10 according the first embodiment of the present invention.

FIG. 1B is an enlarged front view of the frame assembly 25.

FIG. 2 is a longitudinal cross-sectional plan view of the axial flow fan 10 taken along line 2-2 of FIG. 1A illustrating the shutter assembly 39 in open position.

FIG. 3A is a vertical cross-sectional view taken along line 3-3 of FIG. 1A illustrating the shutter assembly 39 in open position.

FIG. 3B is an enlarged plan view of the support 46, gears 48A and 48B.

FIG. 4 is a front view of the propeller 20A.

FIG. 5 is a section along line 5-5 of FIG. 4 showing the guiding fins 35F and 38F.

FIG. 6. is a view partially section of bearing housing 23, bearing 22, shaft 21, hub 36.

FIG. 7 is a plan view partially in section of the centrifugal mechanism 33 with the shutter assembly 39 in a closed position.

FIG. 8 is a plan view partially in section of the centrifugal mechanism 33 with the shutter assembly 39 in an open position.

FIG. 9A is a fragmentary plan view of the axial fan 10″ according the second embodiment of the present invention. The doors 41″ and 42″ are shown in open position and the motor 27 is not shown for clarity.

FIG. 9B is a fragmentary plan view in larger scale of the rotatably connection of the doors 41″ and 42″.

FIG. 9C is a side elevation of FIG. 9B

FIG. 10 is a fragmentary plan view partially in section of the axial flow fan 10″. The doors 41″ and 42″ are shown in their closed position. The drive motor 27 is not shown for clarity.

FIG. 11 is vertical section view of the axial flow fan 10″ taken along line 11-11 of FIG. 9A.

FIG. 12 is a front view (discharge side) of the axial flow fan 300 according to a third embodiment of the present invention.

FIG. 13A is a sectional view of the axial fan 300, taken along line 13-13 of FIG. 12 with the pair of vanes 341 open.

FIG. 13B is a sectional view of the fan 300 taken along line 13-13 of FIG. 12 with the pair of vanes 341 closed.

FIG. 14 is an elevation of propeller 20B.

FIG. 15 is a section of FIG. 14 along lines 15-15 of FIG. 14.

FIGS. 16A and 16B show a detail of the geared hinged connection 341G of the pair of geared vanes in the closed and open configuration, respectively.

FIG. 17A is a front view of the air output end of the axial flow fan 400 according to a fourth embodiment of the invention illustrating the shutter assembly 439 in closed position.

FIG. 17B is a front view of the air output end of the axial flow fan 400 according to a fourth embodiment of the invention, illustrating the shutter assembly 439 in open position. The fan bracket 25″ and the motor 27 are not shown for clarity.

FIG. 18 is a sectional view of the fan 400 taken along line 18-18 of FIG. 17A.

FIG. 19 is a sectional view of the fan 400 taken along line 19-19 of FIG. 17A. The drive motor 27 is not shown for clarity.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will be now described by way of example with reference to the accompanying drawings in which like reference numerals are used throughout the various views to indicate identical elements.

Referring now to the drawings in detail, and initially to FIGS. 1A, 1B, 2, 3A, 4, 5 and FIG. 6 thereof, an axial flow fan assembly 10, constructed in accordance with a first preferred embodiment of the present invention, is illustrated.

The axial flow fan 10 is a high efficiency fan suitable to move efficiently large quantities of dusty and corrosive air in “hostile environments” such as agricultural, chemical and industrial buildings. The fan is preferably a belt driven propeller fan including a compact housing 11 having a cylindrical cavity defining an air flow passageway axially extending about a central axis CL1.

Housing 11 comprises an air intake end 12 with a mounting flange 12 F, a spaced apart air output or discharge end 13 with a flange 13F for fastening with mechanical fasteners 14 a discharge cone 15 equipped with a safety guard 16 positioned at the cone exit face. The guard 16 is made of heavy galvanized steel wire having large openings to allow free airflow therethrough.

The air intake end 12 includes a removable streamlined bell mouth 17 secured with mechanical fasteners 17B thereto. The bell mouth 17 comprises a curved wall defining a convex interior surface, preferably elliptical in cross-section, such to direct smoothly ambient air into the fan housing 11.

Further said bell mouth 17 is provided with a safety guard 18 secured to housing 11 with quick release clips (not shown). The safety guard 18 is positioned at the inlet area of the bell mouth 17. It is preferably made of galvanized circular wires comprising large size openings, to allow free air flow therethrough.

The bell mouth 17 can be made of one piece with the fan housing 11 by a conventional rotational moulding technique or may be formed of fibreglass, etc. The space designed 19 in FIG. 1 is a display space and accommodates a label which may have imprinted thereon the trademark of the fan.

For corrosive environments the fan housing 11 may be formed of a corrosion resistant material such as fiberglass or may be made of light gauge stainless steel rolled from a flat plate into a cylindrical shape to form the hollow body and the flanges 12F and 13F which extend radially and circumferentially along the hollow body ends. The flanges 12F and 13F reinforce substantially the structure of the housing 11 and provide a suitable anchor for the installation of the axial flow fan 10 to the building.

FIGS. 4, 5 and 6 show a propeller 20A secured to shaft 21 that is journaled on a double row angular contact ball bearing 22 fitted into a bearing case 23. The ball bearing 22 is a permanently lubricated type of bearing and comprises a pair of adjacent inner rings that are fitted over the shaft 21 and an outside ring that is fitted into the bearing case 23 and is axially secured on the shaft 21 with snap ring 23S. Said bearing case 23 is normally made of extruded aluminum and comprises a plurality of radial extending lugs 23L fastened with mechanical fasteners 24 to a frame 25 or fan bracket that is made of four intersecting arms extending radially toward a central locus including the bearing case 23. The frame 25 comprises a pair of vertical arms 25V and a pair of horizontal arms 25R made of streamlined aluminium extrusion comprising airfoil shaped wings 25W. The arms 25V and 25R are welded at each respective ends to plates 25P which are fastened with mechanical fasteners 26 to four opposite sides of the air intake end 12 of the fan housing 11.

A drive motor 27 is fastened with mechanical fasteners 27B to a pair of L shaped support plates 28 which are slidably mounted and secured with mechanical fasteners 28B to the frame arm 25V. The drive motor 27 is provided with a pulley 29 over which passes a drive toothed belt 30. The weight of the motor 27 pulls the belt downwardly tensioning it automatically. The motion of the pulley 29 is transmitted to the toothed belt 30 and to fan pulley 31 which is keyed in one end of the shaft 21 and locked in place by lock nut 32 which in the meantime locks the inner rings of the ball bearing 22 against shoulder 21S of the hollow shaft 21.

A centrifugal mechanism 33 is secured with set screws 34 to said shaft 21 and is positioned adjacent to the propeller 20A.

Referring to FIGS. 4, 5 and FIG. 6 it is depicted the propeller assembly 20A which comprises four airfoil shaped blades 35 having a stem 35S rotatably secured to a hub 36 comprising half portions 36A and 36B held together with screws 37 for locking said airfoil shaped blades 35 at the designed pitch.

The blades 35 extend radially outwardly from the hub 36 to the blade tips. Each of said blades comprises at least a pair of guiding fins 35F and a radial adjustable shoe 38 comprising a guiding fin 38F positioned on the front face of said propeller blades 35 such to guide the air flow and reduce the tip blade clearance with the housing 11, so that less air will flow back through said propeller blades tips.

Shape and dimensions of blades 35 and shoes 38 have been thought to ensure a uniform air flow with reduced whirls and dispersions, contributing to increased fan efficiency and reduction of vibrations and noise.

The fan 10 further comprises a shutter assembly 39 or back draft damper fastened with mechanical fasteners 40 to flange 13F.

The shutter assembly 39 comprises a pair of vertically pivoted doors comprising a master door 41M and a slave door 42S extending vertically across the discharge end 13. The doors 41M and 42S are semi circular in form, parallel with one another, their adjacent leading edges are secured with mechanical fasteners 43 respectively to shafts 44M and 45S which are pivotally mounted at their opposite ends to a top bearings 46 and to a bottom bearing 47 which are made of plastic and are fastened with mechanical fasteners 40 to top and bottom portion of the flange 13F. The shutter doors are gearingly coupled by means of meshing gears 48A and 48B which are keyed to the top ends of respective shafts 44M and 45S, and are protected with a guard 49G as depicted in FIG. 3 A and 3B.

In addition, the applicant provides an extension biasing means 50 connected to a support 51 secured to the fan housing 11 and to a crank 52 which is secured to the bottom end of the shaft 44M. When the doors 41M, 42S are in their closed position said extension biasing means 50 urge said doors against a seal 53 that is secured to the flange 13F. When the doors are in their open position the extension biasing means 50 lock said doors one against the other to prevent vibrations.

The master door 41M as well the slave door 42S are made of aluminium or galvanized steel or of one-piece of roto-moulded plastic comprising an internal cavity filled with at least ¾″ thick high grade insulated material. As the shutter doors 41M, 4 are insulated and biased against the seal 53 they will effectively block heat transfer. In addition, each door 41M and 42S comprises at least two guiding fins 41F and 42F positioned symmetrically relative to the propeller's rotational axis CL1. The above depicted doors 41M, 42S are positioned adjacent said propeller 20A and help on straightening any swirls and circular motion of the air flow.

As best seen in FIG. 7 and FIG. 8, a centrifugal mechanism 33 is provided to operate said doors 41M and 42S The centrifugal mechanism 33 comprises a steel hollow guide 54 fixed with a pair of set screws 34 to the shaft 21, a bifurcated collar 54C comprising at least a pair of lugs 54L clamped with bolts 55 to the guide 54, a reciprocating actuator member 56 made preferably of one piece of moulded plastic comprising at least a pair of lug 57L. The reciprocating actuator member 56 is slidably mounted on said hollow guide 54. Said lugs 54L and 57L are pivotally connected with mechanical fasteners 58 to a pair of links 59 and 60 which are symmetrically spaced apart in relation to the propeller's axis of rotation CL1. The links 59 are preferably made of flat aluminium bar and the links 60 are preferably made of steel. The links 60 comprise centrifugal masses 61 fastened with mechanical fasteners 62 on the outermost free ends thereof. The links 59 and 60 are pivotally connected to each other with mechanical fasteners 63 and are able to swing equally in unison toward and away from each other in response to the speed of rotation of the shaft 21 such as to cause axial movement of the reciprocating actuator member 56 toward the master door 41M or away from it. The reciprocating actuator member 56 is thus displaced axially by the centrifugal effect of the weight of the links 60 and centrifugal masses 61 causing a corresponding rotation of the doors 41M and 42S from the closed configuration of FIG. 7 to the wide open configuration of FIG. 8.

A compression biasing means 64 is housed into the hollow guide 54 with one end biased to the inside front wall of the reciprocating actuator member 56 and the other is biased to one end of the shaft 21, as pictured in FIG. 7 and FIG. 8. The reciprocating actuator member 56 comprises a front operative end 56F adapted to frictionally engage and rotate an operating cam 65 that is fastened with mechanical fasteners 66 to the master door 41M and is positioned slightly below the center axis CL1 as shown in FIG. 3A therefore to ease the opening and closing of the doors 41M, 42S.

With reference to FIGS. 9A, 9B, 9C, 10, and FIG. 11, a second embodiment of the present invention is shown and described.

The axial flow fan 10″ of the present invention is similar to the fan 10 herein above described and comprises similar components as the fan 10 of the first embodiment of the invention set above. However, the housing 11″ is more compact than housing 11, a centrifugal mechanism 33″ (similar to the 33) is rotatably connected to the shutter assembly 39″ which comprises a pair of vertically pivoting doors 41″ and 42″ opened and closed by said centrifugal mechanism 33″ that is mounted to one end of a fan hollow shaft 21″ opposite to the propeller 20A and comprises an axial sliding reciprocating actuator member 56″ mounted on a hollow guide 54″. The reciprocating actuator member 56″ comprises a compression operative biasing means 64″ and an operative rod 201 adapted to pass through the fan hollow shaft 21″. The operative rod 201 is threaded and fastened with nut 202 to one end to said reciprocating actuator member 56″ and at the other end is fitted to a ball bearing 203 which is housed into a case 204 comprising two lateral portions 204L connected with pivots 205 to a pair of arms 206 operatively connected with pivots 207 to forks 208 which are secured to a pair of vertically pivoting shutter doors 41″ and 42″ which are pivoting around a stationary rod 209 which extends across the discharge opening 13″ of fan housing 11″ and comprises opposite ends secured to top and bottom supports 211 and 212 secured with mechanical fasteners 213 to flange 13F″ of the fan housing 11″.

When the drive motor 27 is energized, the centrifugal force acting on the centrifugal masses 61 causes the reciprocating actuator member 56″ and the rod 201 to be displaced towards the shutter doors 41″ and 42″, then said rod 201 pushes the bearing 203 and the arms 206 causing the forks 208 to rotate doors 41″ and 42″ around the stationary rod 209 to a wide open position.

When the drive motor 27 is turned off the compression biasing means 64″ pull the operative rod 201 and closes the shutter doors against seal 214.

The shutter doors leading edges may be connected with a continuous “Geared Hinge” 341G which can be made from extruded aluminium. Each door comprises a cavity preferably filled with insulation material, as shown in drawing FIGS. 16A and 16B.

With reference now to FIGS. 12, 13A, 13B, 14 and FIG. 15, a third embodiment of the present invention is illustrated and described. The fan 300 of the present invention comprises a square box housing 311 preferably made of sheet metal rolled with a roll-bending machine. The fan housing 311 comprises an air intake opening 312 provided with flange 312F to which is fastened with mechanical fasteners 317B a bell mouth 317 and a discharge opening 313 with a flange 313F. A propeller 20B is mounted in said fan housing 311 adjacent said air intake opening 312 and is secured to a hollow shaft 21″ that is press-fitted into the inner rings of bearing 22. Said bearing 22 comprises an outside ring that is fitted into a bearing case 23 that is secured to a bracket 25″ (similar to bracket 25 of FIG. 1B) for supporting a propeller 20B mounted on one end of the hollow shaft 21″. The bracket 25″ is secured with mechanical fasteners 25B″to four opposite sides of the air intake opening 312 of the fan housing 311.

The propeller 20B best seen in FIG. 14 and FIG. 15 comprises four airfoil shaped blades 35″ surrounded by an outer band 35D comprising a radial extending portion 35R positioned adjacent a plate 318 that is secured to the fan housing 311 to prevent back airflow.

A centrifugal shutter mechanism 33″ is mounted and secured with set screws 34 to the hollow shaft 21″ opposite to the propeller 20B. It is provided for operating a shutter assembly 339 comprising a plurality of pair of vertical pivoted hinged vanes 341 working in tandem that are vertically mounted across the discharge opening 313 of the fan 300. The vanes 341 are operatively connected to an axial sliding reciprocating spreader bar 342 operatively connected to an operative rod 201 connected to the actuator member 56″. The leading edges of the vanes 341 are pivotally connected with a continuous hinge 341H as best shown on drawing FIG. 12 or a continuous geared hinge 341G as shown in FIGS. 16A and 16B. The continuous hinge 341H comprises a stationary rod 209″ fastened at each opposite ends with mechanical fasteners means 341B to top and bottom flange 313F of the fan housing 311. It is to be understood that the pair of vanes 341 that can be mounted at the fan intake 312 and may be shaped in such a way that when they are in open position their trailing edges will be biased one against each other forming an aerodynamic profile like for example NACA 27-212 such to reduce pressure losses thereof.

With reference now to FIGS. 17A, 17B, FIG. 18 and FIG. 19 a fourth embodiment of the present invention is illustrated and described. The axial flow fan 400 of the present invention comprises a cylindrical shaped housing 411 comprising an air intake end 412 and an air output end 413. The fan housing 411 is preferably made of one-piece of rolled steel or aluminium sheet metal. The air intake end 412 is provided with a bell shaped mouth 17 secured with mechanical fasteners 17B thereto and is provided with a bracket 25″ (similar to the bracket 25 of FIG. 1B) secured with mechanical fasteners 25B″ to four opposite sides of said air intake end for supporting a propeller 20A best shown in FIGS. 4, 5 and 6).

A shutter assembly 439 is mounted at the fan discharge end 413 and comprises a plurality of even angularly spaced pair of vanes 414 comprising leading edges connected to each other with a hinge 414H comprising four intersecting rods including a horizontal stationary rod 209″R and a stationary vertical rod 209″V having opposite ends fastened with mechanical fasteners 413B to four opposite sides of the flange 413F of said fan housing 411. The stationary rods 209″R and 209″H are connected to a central rim 415 near their middle thereof.

A centrifugal actuator 33″ (identical to the one afore depicted) is rotatably connected to the shutter assembly 439 and comprises a reciprocating actuator 56″ provided to open and close simultaneously all vanes 414 which are connected with pivoted means (similar to the ones of FIGS. 9B, 9C) to a rigid frame 417 comprising a central bearing case 418 comprising a ball bearing 419. The opposite ends of said frame 417 are operatively connected to the vanes 414 via forks 420, pivots 420P, arms 421 and pivots 421P. The frame 417 is rotatably connected via the ball bearing 419 to the operative rod 201 that is connected to the actuator member 56″.

The centrifugal mechanism of the present invention permits to operate the shutters at relatively low fan speed. In the cooling system the total air flow volume of the fan shall match the system air volume requirements of the cooling system that vary over time with the temperature and other parameters. In this regard, it is usually advantageous to vary and reduce the air flow of the fans, so that the power requirements of the fans may be reduced.

While the foregoing is directed to various embodiments of the present invention, other and further embodiments may be devised without abandoning the spirit of the invention. For example, the various embodiments of the invention can be included in combination with each other to produce other variations of the disclosed embodiments.

For operating the shutters the applicant shows a centrifugal mechanism but any other device may be adapted to work with the novel aerodynamic pair of vanes working in tandem. Accordingly, the disclosed and illustrated embodiments herein should be considered as exemplary rather than restrictive of the invention which is defined in the accompanying claims. 

1-18. (canceled)
 19. A fan for use in ventilation of a building comprising: a housing and said housing having an interior passageway extending along an axis in an axial direction between an air intake end and a spaced apart air discharge end; a bracket supporting a fan assembly and said bracket being supported by four intersecting arms fixed to four opposite sides of said fan housing intake end; each of said arms extending radially toward a central locus having a rigid case and said case having bearing means and means for connecting said arms thereto; a shaft rotatably journaled into said bearing means; a drive motor having a drive toothed pulley transmitting power to a propeller and said propeller having a plurality of airfoil shaped blades radially extending outwardly from said shaft toward tips portion thereof; said blades further having guiding fins members formed on a front face thereof; a bell shaped intake mounted at said air intake end; an outlet cone mounted at said discharge end; a shutter assembly having a pair of shutter hinged doors diametrically extending across said output end; said doors being connected with a pair of gears for unison movements in opposite direction and comprised of a master door having a convex shaped cam mounted near the middle thereof, and; slave doors disposed next to one another having their leading edges journaled on top and bottom bearings to rotate said slave doors toward said discharge cone.
 20. The fan as in claim 19, wherein said propeller comprises a plurality of airfoil shaped blades; each of said aifoil shaped blades comprising at least a pair of guiding fins members formed on a front face thereof wherein said blades tips portion comprise a radially adjustable shoe having an air flow guiding fin extending circumferentially to fully encircle said tip portion of said blades for preventing air flow returns upstream from said propeller blades and for preventing turbulent flow around said blade tips.
 21. The fan as in claim 19, wherein a 12″ deep bell shaped intake is mounted at said intake end of said fan housing and a discharge cone at said output end thereof.
 22. The fan as in claim 19, wherein said shutter doors are one-piece construction made of rigid, non-corrosive material and comprise an internal cavity with insulation material to prevent conduction heat losses and further comprising an outer portion surface adapted to contact and press seal means mounted at said discharge end of said fan housing, wherein said seal means are compressed by biasing means associated to a centrifugal device to prevent convection heat losses
 23. The fan as in claim 19, wherein said fan assembly has a centrifugal shutter mechanism mounted at one end of said rotating shaft wherein said centrifugal mechanism has at least a pair of short and long links pivotally connected to each other, at least a pair of centrifugal masses equally spaced apart relative to said fan rotational axis, secured to said long links operatively connected to a reciprocating actuator mounted on a guiding hollow shaft coaxially with said fan rotational axis adjacent said master door comprising a convex shaped cam mounted thereon, said axial sliding actuator further comprising an internal operative compression biasing means and an operative end located proximal of said master door convex shaped cam said actuator being movable between an outwardly position frictionally engaging said convex shaped cam to rotate and shut said master door and said slave door so that said doors are biased against seal means to prevent the passage of air through said fan outlet housing and an inwardly position away from said master door for causing the fully opening of said doors in response to the rotation of said propeller.
 24. A fan as in claim 23 wherein said centrifugal mechanism has an axially slidable actuator having an operative end including a ball thrust bearing interposed between said operative end and said shutter hinged doors for rotatably connecting said doors for pushing or pulling them from a first position wherein said shutter assembly closes off the air passageway to a second position wherein air is permitted to flow throughout said fan housing.
 25. A fan for use in a building for ventilation comprising: a box type housing with an interior cavity extending along an axis, an air intake end, a spaced apart air output end, a bracket having four arms fixed at each respective ends to four opposite sides across said housing air intake end, wherein said arms extends inwardly to a central locus having a bearing case comprised of four lugs projecting outwardly therefrom and connecting said four arms; said bearing case having bearing means and a hollow fan shaft rotatably journaled into said bearing means; a drive motor with a drive toothed pulley for transmitting power via a toothed belt to a propeller pulley secured to said fan hollow shaft; a propeller comprising a central split hub and a plurality of airfoil shaped blades including a pair of guiding fin members formed on a front face of said propeller blades; said blades comprising a rigid stem journaled into said split hub which is secured to on one end of said fan hollow shaft; said propeller having blades extending radially outwardly from said central split hub and rotatably therewith, wherein said propeller blades comprises means for assisting in keeping the air flow with a minimum of vortices so as to reduce the turbulence in the air flow through the fan passageway and prevent vibrations, noise and wear of associated shutters positioned down stream or upstream at close distance from said propeller.
 26. The fan as in claim 25 wherein said propeller blade means comprise a plurality of fins positioned at a distance from said rotation axis of said propeller and wherein each propeller blade being entirely surrounded by an outer band comprising a small bell mouth having a flanged inlet end, extending radially, positioned adjacent an orifice plate fixed to said fan housing such as to form a small radial clearance to restrict the flow of air exited from said fan therefore for preventing backflow from downstream to upstream of said ducted propeller.
 27. The fan as in claim 25, further comprising a shutter assembly mounted therein said fan housing across said input air intake or across said air output of said housing, wherein said shutter assembly comprises a plurality of hinged vanes adapted to be mounted vertically or horizontally across said inlet or outlet of said fan housing, preventing, when they are mounted vertically dust accumulation thereon, wherein each pair of vanes leading edges are pivotally connected with a continuous hinge such that each pair of vane is more rigid preventing vibrations thereof.
 28. The fan as in claim 27 wherein said vanes are made of extruded aluminium or plastic comprising cavities filled with insulating material and a longitudinal extending gear to synchronize said vanes so as to simultaneously dose or open said vanes.
 29. The fan as in claim 26 wherein said vanes of said shutter assembly being operatively connected to a centrifugal mechanism connected for rotation to said propeller rotating shaft, wherein said centrifugal mechanism includes at least a pair of links pivotally connected to each other and comprising centrifugal masses equally spaced apart relative to said fan rotational axis, operatively connected to an axially sliding reciprocating actuator mounted on a guiding hollow shaft coaxially with said fan axis of rotation, positioned adjacent to said shutter assembly, said axial sliding actuator further comprising an internal compression biasing means and an operative end comprising a push/pull actuator rod secured to a bearing case comprising a ball bearing, said operative actuator rod being movable between an outwardly position to rotate and shut said vanes by the biasing force of said internal compression biasing means to firmly close said vanes and prevent the passage of air through said fan housing and an inwardly position away from said shutter assembly for causing the fill opening of said vanes in response to the rotation of said propeller.
 30. A fan for use in a building for ventilation, comprising: a housing having a square or round intake end with an interior cavity extending along an axis, a spaced apart round air output end, a bracket having four arms fixed at each respective ends to four opposite sides across said housing air intake end, wherein said arms extend inwardly to a central locus having a bearing case having four lugs projecting outwardly therefrom and connecting said four arms; said bearing case comprising bearing means and a fan hollow shaft rotatably journaled into said bearing means; a drive motor with a drive toothed pulley for transmitting power via a toothed belt to a propeller pulley secured to said fan hollow shaft; a propeller comprising a central split hub and a plurality of blades including a rigid stem for rotatably journaling them into said split hub secured on one end of said hollow fan shaft; said propeller having blades extending radially outwardly from said central split hub and rotatably therewith, wherein said propeller blades comprises means for assisting in keeping the air flow with a minimum of vortices so to prevent vibrations, noise and wear of an associated shutters positioned downstream or upstream at close distance with said propeller wherein said shutter comprises a plurality of hinged vanes angularly spaced working in tandem wherein each vane comprise a leading edge rotating around a common round stationary shaft secured at both ends to said flanged output end of said fan housing and to a central rim supporting said shafts and said vanes wherein said vanes are pivoting between a fully open configuration in which said output opening is open to a closed configuration closing said output opening against seal means.
 31. The fan as in claim 30 wherein said angularly even spaced vanes are open and aligned to the air flow and maintained positively open by centrifugal action of a centrifugal actuator wherein said straight vanes positioned adjacent said propeller assist to control the residual swirl of the air exiting said propeller providing a more efficient fan and less noisy fan.
 32. The fan as in claim 31 wherein said vanes are insulated vanes and wherein said leading edge of said vane is continuously connected with said leading edge of said adjacent vane.
 33. The fan as in claim 32 wherein said pair of vanes when open take the shape of a single aerodynamic shaped vane having a NACA profile such as to cause a decrease of noise and a decrease of drag of said vanes. 